Tower packing is the key component of packed columns. It provides an effective phase interface for the heat and mass transfer between two phases of gas and liquid. Only excellent performance tower packing works with ideal column internals can constitute a technologically advanced packed column.
By improving the uniform distribution of fluid and transfer efficiency, reducing flow resistance and increasing fluid flow flux, the tower packing meet various needs including consumption reduction, energy saving, equipment amplification, high purity product preparation,etc. At present, the development of tower packing, in addition to the study of a variety of structured packing and random packing structures, we also study the packing material, processing methods, surface properties, etc.
Tower packing comes in a variety of types and structures. For the same production operation, various types of packing can be used, this may confuse users and make them hard to choose.
The selection of material depends on the physical properties of the materials to be processed (corrosivity, surface tension, etc.), and operating conditions (temperature, pressure). Besides, bed weight, load bearing capacity, ease of installation and maintenance, as well as pressure drop, flux, efficiency and investment size are also closely related.
Taking the commonly used Pall rings as an example, for the same specific surface area, the weight ratio of ceramics, metals, and plastics is approximately 8:4.5:1. The ceramic material has the smallest porosity, while metals and plastics are similar.
Random packing has advantages such as easy filling, easy cleaning, strong adaptability, and convenient processing. However, a common challenge during use is how to ensure maximum wetting of the packing surface. To achieve this goal, it is necessary to maintain a uniform bed packing, especially in the column wall area, meanwhile ensuring good initial distribution of liquid and gas.
Structured packing, although generally higher in investment compared to random packing, overcomes the disadvantages of random packing. It has the minimum unit theoretical stage pressure drop and is suitable for situations that require the lowest energy consumption and multiple stages of separation processes. For separations involving heat-sensitive systems, structured packing can achieve the lowest temperature of the tower bottom.
Commonly used nominal diameters for random packing in industry are usually 16/25/38/50/76 mm. Generally, the larger packing diameter, the lower pressure drop and efficiency.
In addition, the specific surface area of structured packing can be categorized as 125/250/350/450/500/700 m2/m3. The larger the specific surface area of the packing, the higher the pressure drop and efficiency. The selection of packing should be based on a balance between technical and economic indicators. It is important to note that the ratio of column diameter to packing diameter should not be less than 10 for random packing.
The selection of shape/structure is the most challenging and can only be determined through analysis of its characteristics and practical experience.
